Comment 40 for bug 1861359

$ uname -a
Linux millbarge 5.4.0-12-generic #15-Ubuntu SMP Tue Jan 21 15:12:29 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
$ grep FTRACE /boot/config-`uname -r`
CONFIG_KPROBES_ON_FTRACE=y
CONFIG_HAVE_KPROBES_ON_FTRACE=y
CONFIG_STM_SOURCE_FTRACE=m
# CONFIG_PSTORE_FTRACE is not set
CONFIG_HAVE_DYNAMIC_FTRACE=y
CONFIG_HAVE_DYNAMIC_FTRACE_WITH_REGS=y
CONFIG_HAVE_FTRACE_MCOUNT_RECORD=y
CONFIG_FTRACE=y
CONFIG_FTRACE_SYSCALLS=y
CONFIG_DYNAMIC_FTRACE=y
CONFIG_DYNAMIC_FTRACE_WITH_REGS=y
CONFIG_FTRACE_MCOUNT_RECORD=y
# CONFIG_FTRACE_STARTUP_TEST is not set

$ sudo ls -l /sys/kernel/debug/tracing/available_filter_functions
ls: cannot access '/sys/kernel/debug/tracing/available_filter_functions': No such file or directory
$ sudo kprobe-perf -s 'p:shrink_node'
ERROR: func shrink_node not in /sys/kernel/debug/tracing/available_filter_functions.
Either it doesn't exist, or, it might be unsafe to kprobe. Exiting. Use -F to override.

Are you using secure boot?

$ dmesg | grep -i secure
[ 0.000000] secureboot: Secure boot enabled
[ 0.000000] Kernel is locked down from EFI Secure Boot mode; see man kernel_lockdown.7
[ 0.019867] secureboot: Secure boot enabled
[ 0.965284] integrity: Loaded X.509 cert 'millbarge Secure Boot Module Signature key: effb550c01bc71fba674d2a0b19930ccde197df8'
[ 72.131681] Bluetooth: hci0: Secure boot is enabled

Thanks